JP3384983B2 - Light diffusion sheet and backlight unit using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light diffusing sheet used in a backlight unit incorporated in a liquid crystal display device and a backlight unit using this light diffusing sheet.

[0002]

2. Description of the Related Art As a liquid crystal display device, a backlight system in which a liquid crystal layer is illuminated from the back side to emit light is popular, and a backlight unit is provided on the lower surface side of the liquid crystal layer. As shown in FIG. 4A, such a backlight unit 20 generally includes a rod-shaped lamp 21 as a light source, and a rectangular plate-shaped light guide plate 2 arranged so that an end portion is along the lamp 21.
2 and the light diffusion sheet 2 disposed on the front surface side of the light guide plate 22.
3 and a prism sheet 24 arranged on the surface side of the light diffusion sheet 23.

The function of the backlight unit 20 will be described. First, a light beam incident on the light guide plate 22 from the lamp 21 is reflected by reflection dots or reflection sheets (not shown) on the back surface of the light guide plate 22 and each side surface. The light is emitted from the surface of the light guide plate 22. The light beam emitted from the light guide plate 22 enters the light diffusion sheet 23, is diffused, and is emitted from the surface of the light diffusion sheet 23. After that, the light rays emitted from the light diffusion sheet 23 are incident on the prism sheet 24, and are emitted by the prism portion 24 a formed on the surface of the prism sheet 24 as a light ray having a distribution showing a peak in a substantially upward direction. Thus, the light beam emitted from the lamp 21 is
The light is diffused by the light diffusing sheet 23, and is refracted by the prism sheet 24 so as to show a peak in a substantially upward direction, and further illuminates the entire liquid crystal layer (not shown) above.

Although not shown, there is also a backlight unit in which a light diffusing sheet or a prism sheet is further arranged on the surface side of the prism sheet 24 in consideration of the light condensing characteristic of the prism sheet 24 described above.

As the light diffusing sheet 23 of the backlight unit 20 having the above-mentioned structure, the one in which a base material layer 25 and a light diffusing layer 26 as shown in FIG. 4B are laminated is generally used. The light diffusing layer 26 has a structure in which beads 28 made of synthetic resin, glass or the like are dispersed in a binder 27 made of synthetic resin.

[0006]

The conventional light diffusing sheet 23 and the backlight unit 20 using the same have the following inconveniences. That is, (1) According to the conventional light diffusion sheet 23, in order to improve the light diffusion performance of the light diffusion layer 26, it is necessary to increase the number of beads 28 per unit area. When the beads 28 are provided in a single layer on the surface of the base material layer 25,
The number of beads 28 per unit area is limited due to the size of the beads 28, and as a result, there is also a predetermined limitation in improving the light diffusion performance.

(2) On the other hand, if the beads 28 are stacked on the surface of the base material layer 25 in multiple layers, the beads 2 per unit area are
Although the number of eight can be increased, the light diffusion layer 26
Is difficult to apply and the backlight unit 20
This is against the demand for thinness imposed on itself.

(3) Further, the above conventional light diffusion sheet 23.
According to the above, the beads 28 are projected from the binder 27,
By forming irregularities on the surface of the light diffusion layer 26, it is possible to improve the light diffusion performance, but if the irregularities on the surface of the light diffusion layer 26 are increased, conversely, the total light transmittance of the light diffusion sheet 23 decreases. The inconvenience occurs.

The present invention has been made in view of these disadvantages, and it is possible to improve the light diffusion performance without increasing the density of the beads 28 and also improve the total light transmittance. An object of the present invention is to provide a light diffusion sheet that can be used and a backlight unit using the light diffusion sheet.

[0010]

The invention made to solve the above problems is a light diffusing sheet comprising a light diffusing layer in which beads are dispersed in a binder, and a transparent base material layer, wherein the beads There have a space portion, further, having a space portion
Beads are porous beads, and beads in the space
It is filled with a transparent medium whose refractive index is different from that of the base
It is characterized by being.

According to the above conventional light diffusing sheet, the beads to be used are made of synthetic resin, glass or the like and have a spherical shape. Therefore, a light ray passing through the beads is refracted at two points of incidence and emission. According to the light diffusion sheet, since the beads of the light diffusion layer that imparts the light diffusion performance have the space portion,
The light ray passing through the beads passes through the boundary surface between the base of the bead and the space, and is refracted every time the boundary surface passes in addition to the incident point and the exit point. As a result, the number of refraction times of a light beam that is transmitted is increased as compared with the conventional beads having no space portion, and the light diffusion performance can be dramatically accelerated. Also, as a result of the dramatic increase in light diffusion performance, even if the peak direction of the incident light ray is inclined with respect to the normal direction of the sheet, the inclined peak is alleviated and the light output in the normal direction is increased. Can be made. Furthermore, since the light diffusion performance can be improved without forming the unevenness on the surface like the conventional light diffusion sheet, the total light transmittance can also be improved.

Also, in a light diffusing sheet having a light diffusing layer in which beads are dispersed in a binder, a transparent base material layer, and a sticking prevention layer in which beads are dispersed in a binder in this order, the space portion is similarly formed. It is preferable to use beads having According to the light diffusion sheet, a large light diffusion performance can be imparted to the beads of the sticking prevention layer laminated on the lower surface side, and the light diffusion performance of the entire light diffusion sheet can be increased.

[0013]

Porous beads may be used as the beads having the above-mentioned space. Even with such porous beads, there are many boundary surfaces between the matrix of the beads and the space formed by the porous material, and it is possible to increase the refraction points of the light rays passing therethrough, and as a result, it is possible to increase the light diffusion performance.

[0015]

In the above-mentioned light diffusing sheet, it is preferable to fill the space portion with a transparent medium having a refractive index different from that of the base of the beads. By filling the space portion with a medium different from that of the base, it is possible to prevent deterioration of mechanical properties and the like even if the proportion of the space portion is larger than the above range.

Further, a liquid crystal display device comprising a lamp, a light guide plate which is arranged on a side of the lamp and guides a light beam emitted from the lamp in a front side direction, and a light diffusion sheet which is arranged on a front side of the light guide plate. In the backlight unit for use, the light diffusion sheet of the present invention may be used as the light diffusion sheet. According to the light diffusion sheet of the present invention, it is possible to improve the light diffusion performance, the amount of light emitted in the normal direction, and the total light transmittance as described above. As a result, a liquid crystal display using the backlight unit is obtained. The brightness of the device can be improved.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic sectional view showing a light diffusion sheet. The light diffusion sheet 1 of FIG. 1 includes a base material layer 2, a light diffusion layer 3 laminated on the front side of the base material layer 2,
The sticking prevention layer 4 is laminated on the back surface of the base material layer 2.

Since the base material layer 2 is required to transmit light rays, it is made of a transparent, particularly colorless and transparent synthetic resin. The synthetic resin used for the base material layer 2 is not particularly limited, and examples thereof include polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polycarbonate, polystyrene, polyolefin, cellulose acetate, and weather resistant vinyl chloride. . The thickness of the base material layer 2 is not particularly limited, but is, for example, 10 μm or more and 500 μm or less, preferably 75 μm.
It is set to 250 μm or less. When the thickness of the base material layer 2 is less than the above range, curling may occur easily when the resin composition forming the light diffusion layer 3 is applied. On the contrary, when the thickness of the base material layer 2 exceeds the above range, the brightness of the liquid crystal display device may decrease, and the thickness of the backlight unit becomes large, which violates the demand for thinning of the liquid crystal display device. It will also happen.

The light diffusion layer 3 comprises a binder 5 and beads 6 dispersed in the binder 5. The beads 6 are hollow beads having a substantially spherical shape, and a space portion 9 having a substantially spherical shape is formed therein. The function of the hollow beads 6 will be described. According to the conventional mere spherical beads 28, FIG.
As shown in (a), the transmitted light beam is refracted at two points, an incident point A and an outgoing point B. On the other hand, according to the hollow beads 6, as shown in FIG. 2B, in addition to the incident points A and the emission points B on the outer peripheral surface, the transmitted light rays are incident on the incident points C and the emission points D of the space portion 9. Refracts at 4 points. Therefore, the beads 6
Has significantly higher light diffusion performance than the conventional beads 28.

Examples of the polymer used for the binder 5 include acrylic resin, polyurethane, polyester, fluorine resin, silicone resin, polyamide-imide, epoxy resin and the like. In addition to the above polymers, the binder 5 may be blended with, for example, a plasticizer, a stabilizer, a deterioration inhibitor, a dispersant, or the like. Binder 5
Is transparent because it needs to transmit light rays,
Particularly, colorless and transparent is preferable.

Examples of the material of the beads 6 include acrylic resin, polyurethane, polyvinyl chloride, polystyrene,
Examples thereof include polyacrylonitrile and polyamide. The beads 6 are preferably transparent in order to increase the amount of light rays that pass through the light diffusion sheet 1, and particularly preferably colorless and transparent.

The particle size of the beads 6 is 0.1 μm or more and 100.
μm or less is preferable, and 1 μm or more and 50 μm or less is particularly preferable. This is because when the particle size of the beads 6 is less than the above range, the light diffusion effect becomes insufficient, and conversely, when the particle size exceeds the above range, the coating of the resin composition forming the light diffusion layer 3 is performed. This is because the work becomes difficult. The particle size of the beads 6 is derived by enlarging 100 arbitrarily extracted beads 6 with a microscope, measuring the diameter of the particles, and simply averaging the diameters. When the beads 6 are not spherical, the size of the beads 6 in one arbitrary direction and the size of the beads 6 in the direction orthogonal thereto are averaged.

The content of the beads 6 in the light diffusion layer 3 is preferably 0.1 parts by weight or more and 500 parts by weight or less, and 10 parts by weight or more 3 with respect to 100 parts by weight of the polymer content in the binder 5.
Particularly preferably, it is not more than 00 parts by weight. This is because if the amount is less than the above range, the light diffusion effect becomes insufficient, and conversely, if the amount exceeds the above range, the resin composition for forming the light diffusion layer 3 is coated. This is because the work becomes difficult.

The anti-sticking layer 4 is composed of the binder 7
Further, the beads 8 dispersed in the binder 7 prevent the sticking with the light guide plate (see FIG. 1 ) by the beads 8 protruding from the binder 7. The binder 7 and the beads 8 are the same as those used for the light diffusion layer 3. Therefore, the beads 8 of the sticking prevention layer 4 can also improve the light diffusion performance.

As shown in FIG. 4A, a light guide plate 22, a light diffusion sheet 23 and a prism sheet 24 are laminated to uniformly diffuse the light beam emitted from the lamp 21 on the side of the light guide plate 22 and deflect it upward. When the light diffusing sheet 1 is used as the light diffusing sheet 23 in the backlight unit 20 that is sent to a film (not shown) or the like, the light diffusing sheet 1 has a large light diffusing performance as described above, and therefore the backlight unit 20. The brightness of the liquid crystal display device using can be dramatically improved.

There is also a light diffusion sheet using porous beads 10 as shown in FIG. This porous bead 10 has a substantially spherical shape, and a hole-like space portion 11 is formed on the surface thereof. Since the light beam transmitted through the space 11 is refracted at several places, the porous beads 10 can also improve the light diffusion performance as in the hollow beads 6.

[0028] The light diffusing sheet of the present invention is not limited to the above embodiment, for example, Ru possible der to light diffusion sheet no anti-sticking layer.

[0029]

As described above, according to the light diffusion sheet of the present invention and the backlight unit using the same,
Compared with the conventional light diffusing sheet using only spherical beads, the number of refraction times of the transmitted light beam is increased, and the light diffusing performance can be dramatically accelerated. Also, as a result of the dramatic increase in light diffusion performance, even if the peak direction of the incident light ray is inclined with respect to the normal direction of the sheet, the inclined peak is alleviated and the light output in the normal direction is increased. Can be made. Furthermore, since the light diffusion performance can be improved without forming the unevenness on the surface like the conventional light diffusion sheet, the total light transmittance can also be improved.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a light diffusion sheet according to an embodiment of the present invention.

2A is a schematic cross-sectional view for explaining the transmission of light rays through spherical beads, and FIG. 2B is a schematic cross-sectional view for explaining the transmission of light rays through the hollow beads used in the light diffusion sheet of FIG. Is.

FIG. 3 is a schematic cross-sectional view showing beads having a different form from the beads of FIG.

FIG. 4A is a schematic perspective view showing a general backlight unit, and FIG. 4B is a schematic sectional view showing a general light diffusion sheet.

[Explanation of symbols]

1 Light diffusion sheet 2 Base material layer 3 Light diffusion layer 4 Sticking prevention layer 5 binders 6 beads 7 binder 8 beads 9 space 10 beads 11 space 20 backlight unit 21 lamp 22 Light guide plate 23 Light diffusion sheet 24 Prism sheet 25 Base material layer 26 Light diffusion layer 27 binder 28 beads

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-10-48430 (JP, A) JP-A-5-289075 (JP, A) JP-A-9-127315 (JP, A) JP-A-11- 109113 (JP, A) JP 10-265680 (JP, A) JP 7-218705 (JP, A) Actual development 6-69903 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02B 5/02

Claims (4)

(57) [Claims] 1. A light diffusion sheet comprising a light diffusion layer beads are dispersed in a binder, and a transparent substrate layer, wherein the beads have a space portion, further, beads porous having a space portion Quality beads,
In addition, a transparent medium with a refractive index different from that of the bead base is used in the space.
A light diffusing sheet characterized by being filled with quality . 2. A light diffusion sheet comprising a light diffusion layer in which beads are dispersed in a binder, a transparent base material layer, and a sticking prevention layer in which beads are dispersed in a binder in this order, wherein the beads are spaces. part have a further bead having a space portion is a porous bead,
In addition, a transparent medium with a refractive index different from that of the bead base is used in the space.
A light diffusing sheet characterized by being filled with quality . 3. A bead having the space is an acrylic resin.
The light diffusion sheet according to claim 1 or 2, which is a porous bead made of fat . 4. A lamp, a light guide plate which is arranged laterally of the lamp and guides a light beam emitted from the lamp in a front side direction, and a light guide plate which is arranged on the front side of the light guide plate. A backlight unit for a liquid crystal display device, comprising the light diffusion sheet according to item 1.